1, the first integral problem requires two preparatory knowledge. The first three pictures below answer the first question.

2. The second integral problem is solved by variable substitution-radical substitution.

3. The third integral problem is solved by variable substitution-tangent substitution.

4. The fourth integral problem is solved by variable substitution-sine substitution.

The specific answer is as follows:

The above is the answer to the first question.

The following is the answer to the second question:

The following is the answer to the third question:

The following is the answer to the fourth question: